The chemokine CXCL8 (also known as interleukin-8) plays a key role in innate immunity and inflammation by recruiting neutrophils from the bloodstream to tissue damaged by such insults as bacterial infection. Our long-term goal is to understand the molecular mechanisms of CXCL8 function, and so lay the foundation for new anti-inflammatory treatments. CXCL8 exerts its function by binding to G protein-coupled receptors (GPCRs) on neutrophils, and to glycosaminoglycans (GAGs) on the extracellular matrix and endothelium. A fundamental property of chemokines is the ability to exist reversibly as both monomers and dinners. Therefore, knowledge of CXCL8 monomer and dimer binding to GPCRs and GAGs is critical for understanding in vivo neutrophil recruitment. Our hypothesis is that a dynamic equilibrium among four CXCL8 forms, monomers and dinners in solution and monomers and dinners bound to GAG, regulates in vivo neutrophil recruitment. In this project, we will test our hypothesis by characterizing mutants of trapped monomers and dimers and of native CXCL8 that show reduced binding to either GPCRs or GAGs, and mutants of native CXCL8 that show reduced dimerization potency. We will determine how monomer-dimer equilibrium, and the binding interactions of monomers and dimers for GAGs and GPCRs, regulate in vivo CXCL8 function in animal models (Aim 1). We will determine whether monomers and dinners elicit similar signaling events (but with different potencies), or elicit unique signaling events (Aim 2). Finally, by determining how monomers and dimers bind GAGs, we will better define the distribution of monomers and dimers in solution and bound to GAGs (Aim 3). Innovations in our research design include using a combination of biophysical, in vitro cell-based, and in vivo animal-based studies;novel reagents (trapped monomers and dimers);and a novel microfluid device technology to measure chemotaxis. Lay Abstract: Inflammation plays a central role in the pathology of many vascular and allergic diseases, and of bacterial and viral infections. These diseases cause significant infirmity and mortality, and exact a high economic cost. Current medications either treat the symptoms and not the disease, or are nonspecifically targeted to inhibit the immune and inflammatory responses. New drugs that are highly specific designed on the basis of chemokine function should thus provide better treatments for these diseases.